Tap changers for voltage regulation in uninterrupted switching applications using the principle of reactor switching may include one or more vacuum interrupters to prolong the switching life of the device and avoid fouling the dielectric fluid. Vacuum interrupters have been used in load tap changers to regulate the voltage in power transformers for several decades. In U.S. Pat. No. 3,206,580, McCarty describes an invention mechanically linking one vacuum interrupter and two bypass switches. In U.S. Pat. No. 5,266,759, Dohnal and Neumeyer document substantial improvements to such a system. In these examples, complex linkages are used to transmit actuation forces and mechanically synchronize the tap selector, the bypass switches and the vacuum interrupter, which must all be in close proximity to one another. Thus the tap selector, bypass switches and vacuum interrupter are all built into one large assembly, which complicates manufacturing, assembly, and maintenance processes.
In recent years, alternatives have been proposed to simplify the system by decoupling subsystems and using additional motorized actuators. In U.S. Pat. No. 7,463,010, Dohnal and Schmidbauer describe improvements using separate drive systems for various switching subsystems of the tap changer. Alternatively, in U.S. Patent Publication No. 2011/0297517, Armstrong and Sohail describe a system using two vacuum interrupters, one for each moving contact of the tap selector mechanism, with each vacuum interrupter being actuated by a motorized actuator. Both of these solutions provide substantial improvements to simplify the mechanical systems, however it is the point of the present disclosure to provide further improvements. Dohnal and Schmidbauer's invention maintains a level of mechanical complexity within the vacuum interrupter and bypass switch assembly as it relies upon the use of cams and a parallelogram linkage. The two vacuum-interrupter solution provided by Armstrong and Sohail has cost disadvantages due to the expense of using a second vacuum interrupter as well as a robust drive assembly to overcome contact welding since the vacuum interrupters in such a configuration must be able to withstand fault current loads. For overall cost and performance reasons, the use of one vacuum interrupter with two bypass switches is generally accepted as the preferred method.
As background, FIG. 1 illustrates a typical voltage regulator tap switching circuit 100 for a reactive switching on-load tap changer as is commonly used in a distribution substation transformer. The voltage regulator tap switching circuit 100 includes a tap selector 110, a portion of the series winding 105, a reactor 140 (such as a preventative autotransformer), a switching subassembly 150, and a terminal 165 which could be connected to either the source or load. The series winding 105 is an integral part of the voltage regulator's transformer core and coil assembly. An equalizer winding (not shown) may be included or omitted from the circuit at the designer's discretion. The preventative autotransformer 140 is a separate subassembly as is the tap selector 110.
Within the tap selector 110, there are a plurality of stationary contacts 115 and 120 which are electrically connected to taps in the series winding 105. In certain cases, there may be more stationary contacts connected to the series winding. Movable contacts 125, 130, connect stationary contacts 115, 120 through the preventative autotransformer 140 to the source or load terminal 165.
The switching subassembly 150 consists of bypass switches 152, 154, and a vacuum interrupter 156. The operation of these switches is explained thoroughly in U.S. Pat. No. 5,107,200 to Dohnal and Neumeyer. To actuate and synchronize the switching subassembly 150 to the tap selector switch 110, there is a mechanical linkage 160, which is actuated by an actuator (not shown). The actuator moves the mechanical linkage 160, to position the movable contacts 125, 130 on the appropriate stationary contact to regulate the voltage between the source and load. In practice, the mechanical linkage 160 is a complex design of shafts, gears, cams, bearings and other mechanical components, all of which require a high degree of component-level and assembly-level precision to function properly. Further, the mechanical linkage 160 creates challenges to efficiently packaging the system due to mechanical constraints of power transmission. As a result, there are cost and manufacturing limitations with known voltage regulator solutions.